My U.S. patent application Ser. No. 07/546,252 and U.S. Pat. No. 4,976,709, the entire disclosures of which are incorporated herein by reference, describe methods and apparatus for achieving controlled shrinkage of collagen tissue. These prior inventions have application to collagen shrinkage in many parts of the body, and are particularly useful in an ophthalmological procedure for achieving controlled shape changes in the cornea of the eye for correction of refractive errors.
As described in detail in the application and patent which are incorporated by reference, a presently preferred collagen-shrinkage technique involves use of laser coherent energy in a wavelength range of about 1.80 to about 2.55 microns, or of such coherent infrared energy of wavelengths corresponding to collagen absorption coefficients in the range of about 15 to 120 cm.sup.-1. Irradiation of collagen with such energy is controlled to elevate the collagen temperature to at least 23.degree. C. above normal body temperature to achieve collagen shrinkage.
As explained in my referenced prior disclosures, a critical factor in shrinkage of corneal collagen of the eye is avoidance of excessive tissue-destructive temperature increases throughout the corneal stroma, and especially in the outer epithelial and inner endothelial layers of the cornea. A lowering of the threshold temperature at which collagen shrinkage occurs will provide an added measure of safety in avoiding tissue-destructive temperature increases, and it is to this goal that the present invention is directed.